Mice in Bion-M 1 space mission: training and selection

37-Day microgravity exposure in 16-Week female C57BL/6J mice is associated with bone loss specific to weight-bearing skeletal sites

Exposure to weightlessness in microgravity and elevated space radiation are associated with rapid bone loss in mammals, but questions remain about their mechanisms of action and relative importance. In this study, we tested the hypothesis that bone loss during spaceflight in Low Earth Orbit is primarily associated with site-specific microgravity unloading of weight-bearing sites in the skeleton. Microcomputed tomography and histological analyses of bones from mice space flown on ISS for 37 days in the NASA Rodent Research-1 experiment show significant site-specific cancellous and cortical bone loss occurring in the femur, but not in L2 vertebrae. The lack of bone degenerative effects in the spine in combination with same-animal paired losses in the femur suggests that space radiation levels in Low Earth Orbit or other systemic stresses are not likely to significantly contribute to the observed bone loss. Remarkably, spaceflight is also associated with accelerated progression of femoral head endochondral ossification. This suggests the microgravity environment promotes premature progression of secondary ossification during late stages of skeletal maturation at 21 weeks. Furthermore, mice housed in the NASA ISS Rodent Habitat during 1g ground controls maintained or gained bone relative to mice housed in standard vivarium cages that showed significant bone mass declines. These findings suggest that housing in the Rodent Habitat with greater topological enrichment from 3D wire-mesh surfaces may promote increased mechanical loading of weight-bearing bones and maintenance of bone mass. In summary, our results indicate that in female mice approaching skeletal maturity, mechanical unloading of weight-bearing sites is the major cause of bone loss in microgravity, while sites loaded predominantly by muscle activity, such as the spine, appear unaffected. Additionally, we identified early-onset of femoral head epiphyseal plate secondary ossification as a novel spaceflight skeletal unloading effect that may lead to premature long bone growth arrest in microgravity.

Women in space: A review of known physiological adaptations and health perspectives

Exposure to the spaceflight environment causes adaptations in most human physiological systems, many of which are thought to affect women differently from men. Since only 11.5% of astronauts worldwide have been female, these issues are largely understudied. The physiological nuances affecting the female body in the spaceflight environment remain inadequately defined since the last thorough published review on the subject. A PubMed literature search yielded over 2200 publications. Using NASA's 2014 review series 'The effects of sex and gender on adaptation to space' as a benchmark, we identified substantive advancements and persistent knowledge gaps in need of further study from the nearly 600 related articles that have been published since the initial review. This review highlights the most critical issues to mitigate medical risk and promote the success of missions to the Moon and Mars. Salient sex-linked differences observed terrestrially should be studied during upcoming missions, including increased levels of inflammatory markers, coagulation factors and leptin levels following sleep deprivation; correlation between body mass and the severity of spaceflight-associated neuro-ocular syndrome; increased incidence of orthostatic intolerance; increased severity of muscle atrophy and bone loss; differences in the incidence of urinary tract infections; and susceptibility to specific cancers after exposure to ionizing radiation. To optimize health and well-being among all astronauts, it is imperative to prioritize research that considers the physiological nuances of the female body. A more robust understanding of female physiology in the spaceflight environment will support crew readiness for Artemis missions and beyond.

Using noninvasive imaging to assess manual lymphatic drainage on lymphatic/venous responses in a spaceflight analog

This retrospective case series (clinicaltrials.gov NCT06405282) used noninvasive imaging devices (NIID) to assess the effect of manual lymphatic drainage (MLD) on dermal/venous fluid distribution, perfusion, and temperature alterations of the head, neck, upper torso, and legs while in the 6-degree head-down tilt validated spaceflight analog. A lymphatic fluid scanner measured tissue dielectric constant levels. Near-infrared spectroscopy assessed perfusion, by measuring tissue oxygenation saturation. Long-wave infrared thermography measured tissue temperature gradients. Fifteen healthy, university students participated. NIID assessments were taken 1 minute after assuming the HDT position and then every 30 minutes, with MLD administered from 180 to 195 minutes. Subjects returned to the sitting position and were assessed at post-225 min NIID demonstrated significant changes from baseline (p < 0.01), although these changes at areas of interest varied. MLD had a reverse effect on all variables. NIID assessment supported the potential use of MLD to mitigate fluid shifts during a spaceflight analog.

Microglial activation in spaceflight and microgravity: potential risk of cognitive dysfunction and poor neural health

Due to the increased crewed spaceflights in recent years, it is vital to understand how the space environment affects human health. A lack of gravitational force is known to risk multiple physiological functions of astronauts, particularly damage to the central nervous system (CNS). As innate immune cells of the CNS, microglia can transition from a quiescent state to a pathological state, releasing pro-inflammatory cytokines that contribute to neuroinflammation. There are reports indicating that microglia can be activated by simulating microgravity or exposure to galactic cosmic rays (GCR). Consequently, microglia may play a role in the development of neuroinflammation during spaceflight. Prolonged spaceflight sessions raise concerns about the chronic activation of microglia, which could give rise to various neurological disorders, posing concealed risks to the neural health of astronauts. This review summarizes the risks associated with neural health owing to microglial activation and explores the stressors that trigger microglial activation in the space environment. These stressors include GCR, microgravity, and exposure to isolation and stress. Of particular focus is the activation of microglia under microgravity conditions, along with the proposal of a potential mechanism.

Histoarchitecture of stromal collagen fibers in gastrointestinal hollow organs of mice after a 30-day space flight

The digestive organs are highly sensitive to the influence of orbital flight factors and can limit the professional activities of crew members aboard the International Space Station. Connective tissue, as a system-forming matrix of the integrative-buffer metabolic environment, is of particular relevance in space biomedicine, ensuring the functioning of internal organs under an altered gravitational stimulus. However, the adaptive mechanisms of the fibrous extracellular matrix of the gastric and intestinal connective tissue have not been fully investigated under prolonged microgravity weightlessness. Using histochemical techniques, we experimentally studied the state of collagen fibers in the specific tissue microenvironment of the gastric and intestinal membranes in C57BL/6 N mice after a 30-day space flight, subsequent 7-day ground readaptation, and in animals of the relevant control groups. The 30-day stay of laboratory animals aboard the Bion-M 1 biosatellite resulted in a reduction in the fibrous extracellular matrix of connective tissue in the studied digestive organs, excepting the gastric lamina propria. Increased fibrillogenesis was revealed in the gastrointestinal mucous membranes of animals 7 days after biosatellite landing compared with the parameters of animals in the space flight group. During the experiment with ground simulated orbital flight conditions, changes in collagen fibers were not significant compared to the vivarium control group. Thus, the results obtained evidence gravisensitivity of the fibrous extracellular matrix of the intraorgan connective tissue. This fact also highlights the necessity to further improve gastrointestinal tract-related preventive measures for astronauts during orbital flight.

Active Induction of a Multiple Sclerosis-Like Disease in Common Laboratory Mouse Strains

Experimental autoimmune encephalomyelitis (EAE) is a neuroinflammatory disease with facets in common with multiple sclerosis (MS). It is induced in susceptible mammalian species, with rodents as the preferred hosts, and has been used for decades as a model to investigate the immunopathogenesis of MS as well as for preclinical evaluation of candidate MS therapeutics. Most commonly, EAE is generated by active immunization with central nervous system (CNS) antigens, such as whole CNS homogenate, myelin proteins, or peptides derived from these proteins. However, EAE actually represents a spectrum of diseases in which specific combinations of host/CNS antigen exhibit defined clinical profiles, each associated with unique immunological and pathological features. Similar to MS, EAE is a complex disease where development and progression are also modulated by environmental factors; therefore, the establishment of any given EAE variant can be challenging and requires careful optimization. Here, we describe protocols for three EAE variants, successfully generated in our laboratory, and provide additional information as to how to maintain their unique features and reproducibility.

Morphological changes in motoneurons of the oculomotor nucleus of mice after a 30-day space flight and through a 7-day period of readaptation to earth gravity

The cellular mechanisms of neuroplastic changes in the structure of motoneurons and neuropils of the oculomotor (III) nuclei in mice after a 30-day space flight and 7 days after landing were studied. The results showed that microgravity caused degenerative phenomena in neurons: a decrease in the number of terminal dendritic branches was found both after flight and after readaptation to Earth's gravity. In mice after the flight, the number of axodendritic synapses was less than in the control, and their number was not restored after the readaptation. The number of mitochondria in the motoneurons of animals after the flight also decreased and after the readaptation reached only the control value. In addition, a significant number of dark motorneurons were found in mice after readaptation, which indicates that degeneration was caused not only by microgravity, but also by a reaction to the landing of the biosatellite. On the contrary, in the trochlear nucleus, as we showed earlier (Mikheeva et al. in Brain Res 15(1795):148077. https://doi.org/10.1016/j.brainres.2022.148077 , 2022), after readaptation, the dendrites and synaptic contacts were restored, and mitogenesis is significantly enhanced. It has been suggested that morphological changes in the oculomotor nucleus may be the main cause of microgravity-induced nystagmus.

Smooth Muscle Actin as a Criterion for Gravisensitivity of Stomach and Jejunum in Laboratory Rodents

Smooth muscle tissue (SMT) is one of the main structural components of visceral organs, acting as a key factor in the development of adaptive and pathological conditions. Despite the crucial part of SMT in the gastrointestinal tract activity, the mechanisms of its gravisensitivity are still insufficiently studied. The study evaluated the content of smooth muscle actin (α-SMA) in the membranes of the gastric fundus and jejunum in C57BL/6N mice (30-day space flight), in Mongolian gerbils Meriones unguiculatus (12-day orbital flight) and after anti-orthostatic suspension according to E.R. Morey-Holton. A morphometric analysis of α-SMA in the muscularis externa of the stomach and jejunum of mice and Mongolian gerbils from space flight groups revealed a decreased area of the immunopositive regions, a fact indicating a weakening of the SMT functional activity. Gravisensitivity of the contractile structures of the digestive system may be due to changes in the myofilament structural components of the smooth myocytes or myofibroblast actin. A simulated antiorthostatic suspension revealed no significant changes in the content of the α-SMA expression level, a fact supporting an alteration in the functional properties of the muscularis externa of the digestive hollow organs under weightless environment. The data obtained contribute to the novel mechanisms of the SMT contractile apparatus remodeling during orbital flights and can be used to improve preventive measures in space biomedicine.

The Study of the Caudal Vertebrae of Thick-Toed Geckos after a Prolonged Space Flight by X-ray Phase-Contrast Micro-CT

The proximal caudal vertebrae and notochord in thick-toed geckos (TG) (Chondrodactylus turneri, Gray, 1864) were investigated after a 30-day space flight onboard the biosatellite Bion-M1. This region has not been explored in previous studies. Our research focused on finding sites most affected by demineralization caused by microgravity (G0). We used X-ray phase-contrast tomography to study TG samples without invasive prior preparation to clarify our previous findings on the resistance of TG's bones to demineralization in G0. The results of the present study confirmed that geckos are capable of preserving bone mass after flight, as neither cortical nor trabecular bone volume fraction showed statistically significant changes after flight. On the other hand, we observed a clear decrease in the mineralization of the notochordal septum and a substantial rise in intercentrum volume following the flight. To monitor TG's mineral metabolism in G0, we propose to measure the volume of mineralized tissue in the notochordal septum. This technique holds promise as a sensitive approach to track the demineralization process in G0, given that the volume of calcification within the septum is limited, making it easy to detect even slight changes in mineral content.

Preparation for mice spaceflight: Indications for training C57BL/6J mice to adapt to microgravity effect with three-dimensional clinostat on the ground

Like astronauts, animals need to undergo training and screening before entering space. At present, pre-launch training for mice mainly focuses on adaptation to habitat system. Training for the weightless environment of space in mice has not received much attention. Three-dimensional (3D) clinostat is a method to simulate the effects of microgravity on Earth. However, few studies have used a 3D clinostat apparatus to simulate the effects of microgravity on animal models. Therefore, we conducted a study to evaluate the feasibility and effects of long-term treatment with three-dimensional clinostat in C57BL/6 J mice. Thirty 8-week-old male C57BL/6 J mice were randomly assigned to three groups: mice in individually ventilated cages (MC group, n = 6), mice in survival boxes (SB group, n = 12), and mice in survival boxes receiving 3D clinostat treatment (CS group, n = 12). The mice showed good tolerance after 12 weeks of alternate day training. To evaluate the biological effects of simulated microgravity, the changes in serum metabolites were monitored using untargeted metabolomics, whereas bone loss was assessed using microcomputed tomography of the left femur. Compared with the metabolome of the SB group, the metabolome of the CS group showed significant differences during the first three weeks and the last three weeks. The KEGG pathways in the late stages were mainly related to the nervous system, indicating the influence of long-term microgravity on the central nervous system. Besides, a marked reduction in the trabecular number (P < 0.05) and an increasing trend of trabecular spacing (P < 0.1) were observed to occur in a time-dependent manner in the CS group compared with the SB group. These results showed that mice tolerated well in a 3D clinostat and may provide a new strategy in pre-launch training for mice and conducting relevant ground-based modeling experiments.

Toward countering muscle and bone loss with spaceflight: GSK3 as a potential target

We examined the effects of ∼30 days of spaceflight on glycogen synthase kinase 3 (GSK3) content and inhibitory serine phosphorylation in murine muscle and bone samples from four separate missions (BION-M1, rodent research [RR]1, RR9, and RR18). Spaceflight reduced GSK3β content across all missions, whereas its serine phosphorylation was elevated with RR18 and BION-M1. The reduction in GSK3β was linked to the reduction in type IIA fibers commonly observed with spaceflight as these fibers are particularly enriched with GSK3. We then tested the effects of inhibiting GSK3 before this fiber type shift, and we demonstrate that muscle-specific Gsk3 knockdown increased muscle mass, preserved muscle strength, and promoted the oxidative fiber type with Earth-based hindlimb unloading. In bone, GSK3 activation was enhanced after spaceflight; and strikingly, muscle-specific Gsk3 deletion increased bone mineral density in response to hindlimb unloading. Thus, future studies should test the effects of GSK3 inhibition during spaceflight.

Studying the structure of the nucleus of the trochlear nerve in mice through 7 days of readaptation to earth gravity after spaceflight

The negative effect of hypogravity on the human organism is manifested to a greater extent after the astronauts return to the conditions of habitual gravity. In this work, to elucidate the causes underlying atypical nystagmus, arising after the flight, we studied structural changes in the motoneurons of the trochlear nerve after a 7-day readaptation of mice to the conditions of Earth's gravity. It is known, that motoneurons of the trochlear nerve innervate the muscle that controls the movement of the eyes in the vertical direction. We showed that the number of axodendritic synapses and some other morphological parameters of motoneurons changed by microgravity can return to their original state in 7 days. However, according to some parameters, motoneurons retain a "memory" of the action of microgravity and do not completely restore the structure. The volume of the soma, the shape of the nuclei, the number and orientation of dendrites do not return to pre-flight parameters. The number of dendrites after 7 days of adaptation remained increased, and the proportion of dendrites in the ventrolateral direction became 2.5 times greater than in motoneurons after space flight. The increased number of mitochondria after space flight became even more significant after readaptation. Microgravity-induced plastic changes retain to some extent "memory traces" after readaptation to Earth's gravity. It can be assumed that the restoration of the function of the trochlear nuclei (overcoming nystagmus) is carried out not only by reversible restoration of the structure of neurons, but partially using those mechanisms that are formed in weightlessness.

Spaceflight-Associated Vascular Remodeling and Gene Expression in Mouse Calvaria

Astronauts suffer from a loss of bone mass at a rate of 1.5% per month from lower regions of the body during the course of long-duration (>30 days) spaceflight, a phenomenon that poses important risks for returning crew. Conversely, a gain in bone mass may occur in non-load bearing regions of the body as related to microgravity-induced cephalad fluid shift. Representing non-load bearing regions with mouse calvaria and leveraging the STS-131 (15-day) and BION-M1 (30-day) flights, we examined spatial and temporal calvarial vascular remodeling and gene expression related to microgravity exposure compared between spaceflight (SF) and ground control (GC) cohorts. We examined parasagittal capillary numbers and structures in calvaria from 16 to 23 week-old C57BL/6 female mice (GC, n = 4; SF, n = 5) from STS-131 and 19–20 week-old C57BL/6 male mice (GC, n = 6; SF, n = 6) from BION-M1 using a robust isolectin-IB4 vessel marker. We found that the vessel diameter reduces significantly in mice exposed to 15 days of spaceflight relative to control. Capillarization increases by 30% (SF vs. GC, p = 0.054) in SF mice compared to GC mice. The vessel numbers and diameter remain unchanged in BION-M1 mice calvarial section. We next analyzed the parietal pro-angiogenic (VEGFA) and pro-osteogenic gene (BMP-2, DMP1, RUNX2 and OCN) expression in BION-M1 mice using quantitative RT-PCR. VEGFA gene expression increased 15-fold while BMP-2 gene expression increased 11-fold in flight mice compared to GC. The linkage between vascular morphology and gene expression in the SF conditions suggests that angiogenesis may be important in the regulation of pathological bone growth in non-weight bearing regions of the body. Short-duration microgravity-mediated bone restructuring has implications in planning effective countermeasures for long-duration flights and extraterrestrial human habitation.

Mice display learning and behavioral deficits after a 30-day spaceflight on Bion-M1 satellite

Profound effects of spaceflight on the physiology of humans and non-human animals are well-documented but incompletely explored. Current goals to undertake interplanetary missions increase the urgency to learn more about adaptation to prolonged spaceflight and readaptation to Earth-normal conditions, especially with the inclusion of radiation exposures greater than those confronted in traditional, orbital flights. The 30-day-long Bion M-1 biosatellite flight was conducted at a relatively high orbit, exposing the mice to greater doses of radiation in addition to microgravity, a combination of factors relevant to Mars missions. Results of the present studies with mice provide insights into the consequences on brain function of long-duration spaceflight. After landing, mice showed profound deficits in vestibular responses during aerial drop tests. Spaceflown mice displayed reduced grip strength, rotarod performance, and voluntary wheel running, each, which improved gradually but incompletely over the 7-days of post-flight testing. Continuous monitoring in the animals' home cage activity, in combination with open-field and other tests of motor performance, revealed indices of altered affect, expressed as hyperactivity, potentiated thigmotaxis, and avoidance of open areas which, together, presented a syndrome of persistent anxiety-like behavior. A learned, operant response acquired before spaceflight was retained, whereas the acquisition of a new task was impaired after the flight. We integrate these observations with other results from Bion-M1's program, identifying deficits in musculoskeletal and cardiovascular systems, as well as in the brain and spinal cord, including altered gene expression patterns and the accompanying neurochemical changes that could underlie our behavioral findings.

Cytoskeleton Markers in the Spinal Cord and Mechanoreceptors of Thick-Toed Geckos after Prolonged Space Flights

Spaceflight may cause hypogravitational motor syndrome (HMS). However, the role of the nervous system in the formation of HMS remains poorly understood. The aim of this study was to estimate the effects of space flights on the cytoskeleton of the neuronal and glial cells in the spinal cord and mechanoreceptors in the toes of thick-toed geckos (Chondrodactylus turneri GRAY, 1864). Thick-toed geckos are able to maintain attachment and natural locomotion in weightlessness. Different types of mechanoreceptors have been described in the toes of geckos. After flight, neurofilament 200 immunoreactivity in mechanoreceptors was lower than in control. In some motor neurons of flight geckos, nonspecific pathomorphological changes were observed, but they were also detected in the control. No signs of gliosis were detected after spaceflight. Cytoskeleton markers adequately reflect changes in the cells of the nervous system. We suggest that geckos’ adhesion is controlled by the nervous system. Our study revealed no significant disturbances in the morphology of the spinal cord after the prolonged space flight, supporting the hypothesis that geckos compensate the alterations, characteristic for other mammals in weightlessness, by tactile stimulation.

Micro-CT Study of Mongolian Gerbil Humeral Bone After Prolonged Spaceflight Based on a New Algorithm for Delimitation of Long-Bone Regions

The Mongolian gerbil displays unique physiological and anatomical features that make this species an attractive object for biological experiments in space. However, until recently, the Mongolian gerbil has remained a novel, mostly unstudied animal model in investigating bone loss in weightlessness (G₀). After 12 days of orbital Foton-M3 mission, the humerus of Mongolian gerbils has been studied here via micro-computed tomography (micro-CT) to quantify bone morphometric parameters. The samples from the flight group, delayed synchronous ground-control group, and basal control group were investigated, and main morphometric parameters were reported in the article. The accurate selection of a region of interest is an essential step for a correct assessment of bone parameters. We proposed a new, easy and efficient method for delimiting the bone’s basic regions in the humerus. It is based on quantitative estimation of X-ray attenuation in the cortical bone as a function of humerus bone length. The micro-CT analysis of the basic bone regions revealed a difference in bone morphometric parameters between the flight and control gerbils. The most significant bone loss was observed in the cortical part of the proximal humeral zone in the flight group. No statistically significant changes of volume fraction in the cancellous tissue of proximal and distal epiphyses and metaphyses were observed. A statistically significant increase in both cancellous bone volume and bone X-ray attenuation in the flight group was detected in the proximal part of the diaphyses. We assume that enhanced calcium deposition in the diaphyseal cancellous tissue occurred due to a bone response to G₀ conditions.

Reciprocal Homer1a and Homer2 Isoform Expression Is a Key Mechanism for Muscle Soleus Atrophy in Spaceflown Mice

The molecular mechanisms of skeletal muscle atrophy under extended periods of either disuse or microgravity are not yet fully understood. The transition of Homer isoforms may play a key role during neuromuscular junction (NMJ) imbalance/plasticity in space. Here, we investigated the expression pattern of Homer short and long isoforms by gene array, qPCR, biochemistry, and laser confocal microscopy in skeletal muscles from male C57Bl/N6 mice (n = 5) housed for 30 days in space (Bion-flight = BF) compared to muscles from Bion biosatellite on the ground-housed animals (Bion ground = BG) and from standard cage housed animals (Flight control = FC). A comparison study was carried out with muscles of rats subjected to hindlimb unloading (HU). Gene array and qPCR results showed an increase in Homer1a transcripts, the short dominant negative isoform, in soleus (SOL) muscle after 30 days in microgravity, whereas it was only transiently increased after four days of HU. Conversely, Homer2 long-form was downregulated in SOL muscle in both models. Homer immunofluorescence intensity analysis at the NMJ of BF and HU animals showed comparable outcomes in SOL but not in the extensor digitorum longus (EDL) muscle. Reduced Homer crosslinking at the NMJ consequent to increased Homer1a and/or reduced Homer2 may contribute to muscle-type specific atrophy resulting from microgravity and HU disuse suggesting mutual mechanisms.

Neuro-consequences of the spaceflight environment

As human space exploration advances to establish a permanent presence beyond the Low Earth Orbit (LEO) with NASA's Artemis mission, researchers are striving to understand and address the health challenges of living and working in the spaceflight environment. Exposure to ionizing radiation, microgravity, isolation and other spaceflight hazards pose significant risks to astronauts. Determining neurobiological and neurobehavioral responses, understanding physiological responses under Central Nervous System (CNS) control, and identifying putative mechanisms to inform countermeasure development are critically important to ensuring brain and behavioral health of crew on long duration missions. Here we provide a detailed and comprehensive review of the effects of spaceflight and of ground-based spaceflight analogs, including simulated weightlessness, social isolation, and ionizing radiation on humans and animals. Further, we discuss dietary and non-dietary countermeasures including artificial gravity and antioxidants, among others. Significant future work is needed to ensure that neural, sensorimotor, cognitive and other physiological functions are maintained during extended deep space missions to avoid potentially catastrophic health and safety outcomes.

Intergenerational effect of short-term spaceflight in mice

As space travel becomes more accessible, it is important to understand the effects of spaceflight including microgravity, cosmic radiation, and psychological stress. However, the effect on offspring has not been well studied in mammals. Here we investigated the effect of 35 days spaceflight on male germ cells. Male mice that had experienced spaceflight exhibit alterations in binding of transcription factor ATF7, a regulator of heterochromatin formation, on promoter regions in testis, as well as altered small RNA expression in spermatozoa. Offspring of space-traveling males exhibit elevated hepatic expression of genes related to DNA replication. These results indicate that spaceflight has intergenerational effect.

Cerebellar morphology and behavioural correlations of the vestibular function alterations in weightlessness

In humans and other vertebrates, the range of disturbances and behavioural changes induced by spaceflight conditions are well known. Sensory organs and the central nervous system (CNS) are forced to adapt to new environmental conditions of weightlessness. In comparison with peripheral vestibular organs and behavioural disturbances in weightlessness conditions, the CNS vestibular centres of vertebrates, including the cerebellum, have been poorly examined in orbital experiments, as well as in experimental micro- and hypergravity. However, the cerebellum serves as a critical control centre for learning and sensory system integration during space-flight. Thus, it is referred to as a principal brain structure for adaptation to gravity and the entire sensorimotor adaptation and learning during weightlessness. This paper is focused on the prolonged spaceflight effects on the vestibular cerebellum evidenced from animal models used in the Bion-M1 project. The changes in the peripheral vestibular apparatus and brainstem primary vestibular centres with appropriate behavioural disorders after altered gravity exposure are briefly reviewed. The cerebellum studies in space missions and altered gravity are discussed.

Influence of a 30-day spaceflight on the structure of motoneurons of the trochlear nerve nucleus in mice

During spaceflight and immediately after it, adaptive neuroplastic changes occur in the sensorimotor structures of the central nervous system, which are associated with changes of mainly vestibular and visual signals. It is known that the movement of the eyeball in the vertical direction is carried out by muscles that are innervated by the trochlear nerve (CN IV) and the oculomotor nerve (CN III). To elucidate the cellular processes underlying the atypical vertical nystagmus that occurs under microgravity conditions, it seems necessary to study the state of these nuclei in animals in more detail after prolonged space flights. We carried out a qualitative and quantitative light-optical and ultrastructural analysis of the nuclei of the trochlear nerve in mice after a 30-day flight on the Bion-M1 biosatellite. As a result, it was shown that the dendrites of motoneurons in the nucleus of the trochlear nerve significantly reorganized their geometry and orientation under microgravity conditions. The number of dendritic branches was increased, possibly in order to amplify the reduced signal flow. To ensure such plastic changes, the number and size of mitochondria in the soma of motoneurons and in axons coming from the vestibular structures increased. Thus, the main role in the adaptation of the trochlear nucleus to microgravity conditions, apparently, belongs to the dendrites of motoneurons, which rearrange their structure and function to enhance the flow of sensory information. These results complement our knowledge of the causes of atypical nystagmus in microgravity.

Novel method for evaluating the health condition of mice in space through a video downlink

Clarification of the criteria for managing animal health is essential to increase the reliability of experiments and ensure transparency in animal welfare. For experiments performed in space, there is no consensus on how to care for animals owing to technical issues, launch mass limitation, and human resources. Some biological processes in mammals, such as musculoskeletal or immune processes, are altered in the space environment, and mice in space can be used to simulate morbid states, such as senescence acceleration. Thus, there is a need to establish a novel evaluation method and evaluation criteria to monitor animal health. Here, we report a novel method to evaluate the health of mice in space through a video downlink in a series of space experiments using the Multiple Artificial-gravity Research System (MARS). This method was found to be more useful in evaluating animal health in space than observations and body weight changes of the same live mice following their return to Earth. We also developed criteria to evaluate health status via a video downlink. These criteria, with “Fur condition” and “Respiratory” as key items, provided information on the daily changes in the health status of mice and helped to identify malfunctions at an early stage. Our method and criteria led to the success of our missions, and they will help establish appropriate rules for space experiments in the future.

Human torpor: translating insights from nature into manned deep space expedition

During a long-duration manned spaceflight mission, such as flying to Mars and beyond, all crew members will spend a long period in an independent spacecraft with closed-loop bioregenerative life-support systems. Saving resources and reducing medical risks, particularly in mental heath, are key technology gaps hampering human expedition into deep space. In the 1960s, several scientists proposed that an induced state of suppressed metabolism in humans, which mimics 'hibernation', could be an ideal solution to cope with many issues during spaceflight. In recent years, with the introduction of specific methods, it is becoming more feasible to induce an artificial hibernation-like state (synthetic torpor) in non-hibernating species. Natural torpor is a fascinating, yet enigmatic, physiological process in which metabolic rate (MR), body core temperature (T_b ) and behavioural activity are reduced to save energy during harsh seasonal conditions. It employs a complex central neural network to orchestrate a homeostatic state of hypometabolism, hypothermia and hypoactivity in response to environmental challenges. The anatomical and functional connections within the central nervous system (CNS) lie at the heart of controlling synthetic torpor. Although progress has been made, the precise mechanisms underlying the active regulation of the torpor-arousal transition, and their profound influence on neural function and behaviour, which are critical concerns for safe and reversible human torpor, remain poorly understood. In this review, we place particular emphasis on elaborating the central nervous mechanism orchestrating the torpor-arousal transition in both non-flying hibernating mammals and non-hibernating species, and aim to provide translational insights into long-duration manned spaceflight. In addition, identifying difficulties and challenges ahead will underscore important concerns in engineering synthetic torpor in humans. We believe that synthetic torpor may not be the only option for manned long-duration spaceflight, but it is the most achievable solution in the foreseeable future. Translating the available knowledge from natural torpor research will not only benefit manned spaceflight, but also many clinical settings attempting to manipulate energy metabolism and neurobehavioural functions.

Influence of Microgravity on Apoptosis in Cells, Tissues, and Other Systems In Vivo and In Vitro

All life forms have evolved under the constant force of gravity on Earth and developed ways to counterbalance acceleration load. In space, shear forces, buoyance-driven convection, and hydrostatic pressure are nullified or strongly reduced. When subjected to microgravity in space, the equilibrium between cell architecture and the external force is disturbed, resulting in changes at the cellular and sub-cellular levels (e.g., cytoskeleton, signal transduction, membrane permeability, etc.). Cosmic radiation also poses great health risks to astronauts because it has high linear energy transfer values that evoke complex DNA and other cellular damage. Space environmental conditions have been shown to influence apoptosis in various cell types. Apoptosis has important functions in morphogenesis, organ development, and wound healing. This review provides an overview of microgravity research platforms and apoptosis. The sections summarize the current knowledge of the impact of microgravity and cosmic radiation on cells with respect to apoptosis. Apoptosis-related microgravity experiments conducted with different mammalian model systems are presented. Recent findings in cells of the immune system, cardiovascular system, brain, eyes, cartilage, bone, gastrointestinal tract, liver, and pancreas, as well as cancer cells investigated under real and simulated microgravity conditions, are discussed. This comprehensive review indicates the potential of the space environment in biomedical research.

Possible Mechanisms of Axonal Transport Disturbances in Mouse Spinal Motoneurons Induced by Hypogravity

The data obtained by transcriptome analysis of lumbar spinal cord segments, sciatic nerve, and the respiratory diaphragm of the mice performed after a space flight on board Bion-M1 biosatellite were processed by bioinformatic methods aimed at elucidation of the regularities in hypogravity-induced transcriptome changes in various compartments of motor neurons. The study revealed abnormalities of axonal transport in spinal motor neurons provoked by weightlessness. These data agree with the results of electron microscopy examination of the spinal cord in experimental animals. In space group mice sacrificed on the landing day, the content of perinuclear ribosomes in lumbar motoneurons surpassed that in control mice or in the recovery group examined 1 week after the flight. The data corroborate our hypothesis on contribution of axonal transport disturbances into pathogenesis of hypogravity motor syndrome. They can be employed as a launching pad for further study of hypogravity-triggered motor disorder mechanisms in order to elaborate the preventive therapy against the development of hypogravity motor syndrome in space flights.

Spaceflight and brain plasticity: Spaceflight effects on regional expression of neurotransmitter systems and neurotrophic factors encoding genes

The critical problem of space exploration is the effect of long-term space travel on brain functioning. Current information concerning the effects of actual spaceflight on the brain was obtained on rats and mice flown on five missions of Soviet/Russian biosatellites, NASA Neurolab Mission STS90, and International Space Station (ISS). The review provides converging lines of evidence that: 1) long-term spaceflight affects both principle regulators of brain neuroplasticity - neurotransmitters (5-HT and DA) and neurotrophic factors (CDNF, GDNF but not BDNF); 2) 5-HT- (5-HT_2A receptor and MAO A) and especially DA-related genes (TH, MAO A, COMT, D1 receptor, CDNF and GDNF) belong to the risk neurogenes; 3) brain response to spaceflight is region-specific. Substantia nigra, striatum and hypothalamus are highly sensitive to the long-term spaceflight: in these brain areas spaceflight decreased the expression of both DA-related and neurotrophic factors genes. Since DA system is involved in the regulation of movement and cognition the data discussed in the review could explain dysfunction of locomotion and behavior of astronauts and direct further investigations to the DA system.

Gene-Metabolite Network Linked to Inhibited Bioenergetics in Association With Spaceflight-Induced Loss of Male Mouse Quadriceps Muscle

Prolonged residence of mice in spaceflight is a scientifically robust and ethically ratified model of muscle atrophy caused by continued unloading. Under the Rodent Research Program of the National Aeronautics and Space Administration (NASA), we assayed the large-scale mRNA and metabolomic perturbations in the quadriceps of C57BL/6j male mice that lived in spaceflight (FLT) or on the ground (control or CTR) for approximately 4 weeks. The wet weights of the quadriceps were significantly reduced in FLT mice. Next-generation sequencing and untargeted mass spectroscopic assays interrogated the gene-metabolite landscape of the quadriceps. A majority of top-ranked differentially suppressed genes in FLT encoded proteins from the myosin or troponin families, suggesting sarcomere alterations in space. Significantly enriched gene-metabolite networks were found linked to sarcomeric integrity, immune fitness, and oxidative stress response; all inhibited in space as per in silico prediction. A significant loss of mitochondrial DNA copy numbers in FLT mice underlined the energy deprivation associated with spaceflight-induced stress. This hypothesis was reinforced by the transcriptomic sequencing-metabolomics integrative analysis that showed inhibited networks related to protein, lipid, and carbohydrate metabolism, and adenosine triphosphate (ATP) synthesis and hydrolysis. Finally, we discovered important upstream regulators, which could be targeted for next-generation therapeutic intervention for chronic disuse of the musculoskeletal system. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.

Nrf2 contributes to the weight gain of mice during space travel

Space flight produces an extreme environment with unique stressors, but little is known about how our body responds to these stresses. While there are many intractable limitations for in-flight space research, some can be overcome by utilizing gene knockout-disease model mice. Here, we report how deletion of Nrf2, a master regulator of stress defense pathways, affects the health of mice transported for a stay in the International Space Station (ISS). After 31 days in the ISS, all flight mice returned safely to Earth. Transcriptome and metabolome analyses revealed that the stresses of space travel evoked ageing-like changes of plasma metabolites and activated the Nrf2 signaling pathway. Especially, Nrf2 was found to be important for maintaining homeostasis of white adipose tissues. This study opens approaches for future space research utilizing murine gene knockout-disease models, and provides insights into mitigating space-induced stresses that limit the further exploration of space by humans.

Using Nrf2 knockout mice, Suzuki, Uruno, Yumoto et al. show that space travel activates Nrf2 signaling, which contributes to the weight gain of mice by regulating fat metabolism of white adipose tissues. This study provides insights into potential interventions to mitigate stresses that accompany space travels.

Challenges to the central nervous system during human spaceflight missions to Mars

Space travel presents a number of environmental challenges to the central nervous system, including changes in gravitational acceleration that alter the terrestrial synergies between perception and action, galactic cosmic radiation that can damage sensitive neurons and structures, and multiple factors (isolation, confinement, altered atmosphere, and mission parameters, including distance from Earth) that can affect cognition and behavior. Travelers to Mars will be exposed to these environmental challenges for up to 3 years, and space-faring nations continue to direct vigorous research investments to help elucidate and mitigate the consequences of these long-duration exposures. This article reviews the findings of more than 50 years of space-related neuroscience research on humans and animals exposed to spaceflight or analogs of spaceflight environments, and projects the implications and the forward work necessary to ensure successful Mars missions. It also reviews fundamental neurophysiology responses that will help us understand and maintain human health and performance on Earth.

Validation of a New Rodent Experimental System to Investigate Consequences of Long Duration Space Habitation

Animal models are useful for exploring the health consequences of prolonged spaceflight. Capabilities were developed to perform experiments in low earth orbit with on-board sample recovery, thereby avoiding complications caused by return to Earth. For NASA’s Rodent Research-1 mission, female mice (ten 32 wk C57BL/6NTac; ten 16 wk C57BL/6J) were launched on an unmanned vehicle, then resided on the International Space Station for 21/22d or 37d in microgravity. Mice were euthanized on-orbit, livers and spleens dissected, and remaining tissues frozen in situ for later analyses. Mice appeared healthy by daily video health checks and body, adrenal, and spleen weights of 37d-flight (FLT) mice did not differ from ground controls housed in flight hardware (GC), while thymus weights were 35% greater in FLT than GC. Mice exposed to 37d of spaceflight displayed elevated liver mass (33%) and select enzyme activities compared to GC, whereas 21/22d-FLT mice did not. FLT mice appeared more physically active than respective GC while soleus muscle showed expected atrophy. RNA and enzyme activity levels in tissues recovered on-orbit were of acceptable quality. Thus, this system establishes a new capability for conducting long-duration experiments in space, enables sample recovery on-orbit, and avoids triggering standard indices of chronic stress.

Multiscale effects of spaceflight on murine tendon and bone

Despite a wealth of data on the effects of spaceflight on tendons and bones, little is known about its effects on the interfacial tissue between these two structures, the enthesis. Mice were sent to space on three separate missions: STS-131, STS-135, and Bion-M1 to determine how spaceflight affects the composition, structure, mechanics, and gene expression of the humerus-supraspinatus and calcaneus-Achilles entheses. At the nanoscale, spaceflight resulted in decreased carbonate levels in the bone, likely due to increased remodeling, as suggested by increased expression of genes related to osteoclastogenesis (CatK, Tnfsf11) and mature osteoblasts (Col1, Osc). Tendons showed a shift in collagen fibril size towards smaller diameters that may have resulted from increased expression of genes related to collagen degradation (Mmp3, Mmp13). These nanoscale changes did not result in micro- and milliscale changes to the structure and mechanics of the enthesis. There were no changes in bone volume, trabecular structure, failure load, or stiffness with spaceflight. This lack of tissue-level change may be anatomy based, as extremities may be less sensitive to spaceflight than central locations such as vertebrae, yet results highlight that the tendon enthesis may be robust against negative effects of spaceflight.

Effects of spaceflight on the mouse submandibular gland

OBJECTIVE

This study was conducted to determine if the morphology and biochemistry of the mouse submandibular gland is affected by microgravity and the spaceflight environment.

DESIGN

Tissues from female mice flown on the US space shuttle missions Space Transportation System (STS)-131 and STS-135 for 15 and 13 d, respectively, and from male mice flown on the 30 d Russian Bion-M1 biosatellite, were examined using transmission electron microscopy and light and electron microscopic immunohistochemistry.

RESULTS

In contrast to the parotid gland, morphologic changes were not apparent in the submandibular gland. No significant changes in protein expression, as assessed by quantitative immunogold labeling, occurred in female mice flown for 13-15 d. In male mice, however, increased labeling for salivary androgen binding protein alpha (in acinar cell secretory granules), and epidermal growth factor and nerve growth factor (in granular convoluted duct cell granules) was seen after 30 d in space.

CONCLUSION

These results indicate that spaceflight alters secretory protein expression in the submandibular gland and suggest that the sex of the animals and the length of the flight may affect the response. These findings also show that individual salivary glands respond differently to spaceflight. Saliva contains proteins secreted from salivary glands and is easily collected, therefore is a useful biofluid for general medical analyses and in particular for monitoring the physiology and health of astronauts.

Male mice, caged in the International Space Station for 35 days, sire healthy offspring

The effect on the reproductive system and fertility of living in a space environment remains unclear. Here, we caged 12 male mice under artificial gravity (≈1 gravity) (AG) or microgravity (MG) in the International Space Station (ISS) for 35 days, and characterized the male reproductive organs (testes, epididymides, and accessory glands) after their return to earth. Mice caged on earth during the 35 days served as a “ground” control (GC). Only a decrease in accessory gland weight was detected in AG and MG males; however, none of the reproductive organs showed any overt microscopic defects or changes in gene expression as determined by RNA-seq. The cauda epididymal spermatozoa from AG and MG mice could fertilize oocytes in vitro at comparable levels as GC males. When the fertilized eggs were transferred into pseudo-pregnant females, there was no significant difference in pups delivered (pups/transferred eggs) among GC, AG, and MG spermatozoa. In addition, the growth rates and fecundity of the obtained pups were comparable among all groups. We conclude that short-term stays in outer space do not cause overt defects in the physiological function of male reproductive organs, sperm function, and offspring viability.

Medications in Space: In Search of a Pharmacologist's Guide to the Galaxy

Medications have been used during space missions for more than half a century, yet our understanding of the effects of spaceflight on drug pharmacokinetics and pharmacodynamics is poor. The space environment induces time-dependent alterations in human physiology that include fluid shifts, cardiovascular deconditioning, bone and muscle density loss, and impaired immunity. This review presents the current knowledge on the physiological effects of spaceflight that can translate into altered drug disposition and activity and eventually to inadequate treatment. It describes findings from studies in astronauts along with mechanistic studies in animal models and in vitro systems. Future missions into deeper space and the emergence of commercial spaceflight will require a more detailed understanding of space pharmacology to optimize treatment in astronauts and space travelers.

Individual features of play behavior in thick-toed geckos in weightlessness and normal gravity conditions

The object play behavior in thick-toed geckos (Chondrodactylus turneri GRAY 1864) was studied during a 30-day orbital experiment onboard the Bion-M1 biosatellite. The play object for five geckos was a marking collar that one of the geckos in the flight group removed immediately before the launch. The play behavior started when either the gecko observed the approaching floating collar or when the gecko independently approached the stationary collar, followed by manipulation of the collar and subsequent observation of its moving away. While playing with the collar, the individuality of geckos' behavior was manifested in the frequency and number of play episodes, the nature of manipulations, and the duration of interest in play during the flight. We found that thick-toed geckos could play not only with an unknown object (marking collar) but also with familiar molting skins. In weightlessness, the play behavior of geckos with molting skin fragments was similar to the play behavior with the collar and also varied between individuals. It was established that geckos maintained a similar individual level of play activity with different objects (collar and molting skins). It was found that geckos also played with fragments of molting skin under normal gravity conditions. In contrast to weightlessness, play behavior at normal gravity was rare and limited to short durations of object manipulation.

Bioinformatic Study of Transcriptome Changes in the Mice Lumbar Spinal Cord After the 30-Day Spaceflight and Subsequent 7-Day Readaptation on Earth: New Insights Into Molecular Mechanisms of the Hypogravity Motor Syndrome

The hypogravity motor syndrome (HMS) is one of the deleterious impacts of weightlessness on the human body in orbital space missions. There is a hypothesis that disorders of musculoskeletal system as part of HMS arise in consequence of changes in spinal motor neurons. The study was aimed at bioinformatic analysis of transcriptome changes in lumbar spinal cords of mice after a 30-day spaceflight aboard biosatellite Bion-M1 (space group, S) and subsequent 7-day readaptation to the Earth’s gravity (recovery group, R) when compared with control mice (C group) housed in simulated biosatellite conditions on the Earth. Gene ontology and human phenotype ontology databases were used to detect biological processes, molecular functions, cellular components, and human phenotypes associated with HMS. Our results suggest resemblance of molecular changes developing in space orbit and during the postflight recovery to terrestrial neuromuscular disorders. Remarkably, more prominent transcriptome changes were revealed in R vs. S and R vs. C comparisons that are possibly related to the 7-day recovery period in the Earth’s gravity condition. These data may assist with establishment of HMS pathogenesis and proposing effective preventive and therapeutic options.

Reptiles in Space Missions: Results and Perspectives

Reptiles are a rare model object for space research. However, some reptile species demonstrate effective adaptation to spaceflight conditions. The main scope of this review is a comparative analysis of reptile experimental exposure in weightlessness, demonstrating the advantages and shortcomings of this model. The description of the known reptile experiments using turtles and geckos in the space and parabolic flight experiments is provided. Behavior, skeletal bones (morphology, histology, and X-ray microtomography), internal organs, and the nervous system (morphology, histology, and immunohistochemistry) are studied in the spaceflight experiments to date, while molecular and physiological results are restricted. Therefore, the results are discussed in the scope of molecular data collected from mammalian (mainly rodents) specimens and cell cultures in the parabolic and orbital flights and simulated microgravity. The published data are compared with the results of the gecko model studies after the 12–44.5-day spaceflights with special reference to the unique peculiarities of the gecko model for the orbital experiments. The complex study of thick-toed geckos after three spaceflights, in which all geckos survived and demonstrated effective adaptation to spaceflight conditions, was performed. However, future investigations are needed to study molecular mechanisms of gecko adaptation in space.

Behavior of mice aboard the International Space Station

Interest in space habitation has grown dramatically with planning underway for the first human transit to Mars. Despite a robust history of domestic and international spaceflight research, understanding behavioral adaptation to the space environment for extended durations is scant. Here we report the first detailed behavioral analysis of mice flown in the NASA Rodent Habitat on the International Space Station (ISS). Following 4-day transit from Earth to ISS, video images were acquired on orbit from 16- and 32-week-old female mice. Spaceflown mice engaged in a full range of species-typical behaviors. Physical activity was greater in younger flight mice as compared to identically-housed ground controls, and followed the circadian cycle. Within 7-10 days after launch, younger (but not older), mice began to exhibit distinctive circling or 'race-tracking' behavior that evolved into coordinated group activity. Organized group circling behavior unique to spaceflight may represent stereotyped motor behavior, rewarding effects of physical exercise, or vestibular sensation produced via self-motion. Affording mice the opportunity to grab and run in the RH resembles physical activities that the crew participate in routinely. Our approach yields a useful analog for better understanding human responses to spaceflight, providing the opportunity to assess how physical movement influences responses to microgravity.

Articular cartilage and sternal fibrocartilage respond differently to extended microgravity

The effects of spaceflight on cartilaginous structure are largely unknown. To address this deficiency, articular cartilage (AC) and sternal cartilage (SC) from mice exposed to 30 days of microgravity on the BION-M1 craft were investigated for pathological changes. The flight AC showed some evidence of degradation at the tissue level with loss of proteoglycan staining and a reduction in mRNA expression of mechano-responsive and structural cartilage matrix proteins compared to non-flight controls. These data suggest that degradative changes are underway in the AC extracellular matrix exposed to microgravity. In contrast, there was no evidence of cartilage breakdown in SC flight samples and the gene expression profile was distinct from that of AC with a reduction in metalloproteinase gene transcription. Since the two cartilages respond differently to microgravity we propose that each is tuned to the biomechanical environments in which they are normally maintained. That is, the differences between magnitude of normal terrestrial loading and the unloading of microgravity dictates the tissue response. Weight-bearing articular cartilage, but not minimally loaded sternal fibrocartilage, is negatively affected by the unloading of microgravity. We speculate that the maintenance of physiological loading on AC during spaceflight will minimize AC damage.

Third harmonic generation imaging and analysis of the effect of low gravity on the lacuno-canalicular network of mouse bone

The lacuno-canalicular network (LCN) hosting the osteocytes in bone tissue represents a biological signature of the mechanotransduction activity in response to external biomechanical loading. Using third-harmonic generation (THG) microscopy with sub-micrometer resolution, we investigate the impact of microgravity on the 3D LCN structure in mice following space flight. A specific analytical procedure to extract the LCN characteristics from THG images is described for ex vivo studies of bone sections. The analysis conducted in different anatomical quadrants of femoral cortical bone didn’t reveal any statistical differences between the control, habitat control and flight groups, suggesting that the LCN connectivity is not affected by one month space flight. However, significant variations are systematically observed within each sample. We show that our current lack of understanding of the extent of the LCN heterogeneity at the organ level hinders the interpretation of such investigations based on a limited number of samples and we discuss the implications for future biomedical studies.

Analysis of femurs from mice embarked on board BION-M1 biosatellite reveals a decrease in immune cell development, including B cells, after 1 wk of recovery on Earth

Bone loss and immune dysregulation are among the main adverse outcomes of spaceflight challenging astronauts' health and safety. However, consequences on B-cell development and responses are still under-investigated. To fill this gap, we used advanced proteomics analysis of femur bone and marrow to compare mice flown for 1 mo on board the BION-M1 biosatellite, followed or not by 1 wk of recovery on Earth, to control mice kept on Earth. Our data revealed an adverse effect on B lymphopoiesis 1 wk after landing. This phenomenon was associated with a 41% reduction of B cells in the spleen. These reductions may contribute to explain increased susceptibility to infection even if our data suggest that flown animals can mount a humoral immune response. Future studies should investigate the quality/efficiency of produced antibodies and whether longer missions worsen these immune alterations.-Tascher, G., Gerbaix, M., Maes, P., Chazarin, B., Ghislin, S., Antropova, E., Vassilieva, G., Ouzren-Zarhloul, N., Gauquelin-Koch, G., Vico, L., Frippiat, J.-P., Bertile, F. Analysis of femurs from mice embarked on board BION-M1 biosatellite reveals a decrease in immune cell development, including B cells, after 1 wk of recovery on Earth.

Attachment of Turner's thick-toed geckos (Chondrodactylus turneri GRAY 1864) during weightlessness and their responses to flotation

We investigated the behavior of 15 female Turner's thick-toed geckos (Chondrodactylus turneri GRAY 1864) during a 30-day orbital experiment on the unmanned spacecraft "BION-M" No. 1. During weightlessness, the geckos maintained their ability to attach to the surfaces using the subdigital pads on their toes. On average, the geckos spent 99.9% of the time adhering to surfaces during the flight and only 0.1% floating freely. The active geckos, when starting to float, immediately restored attachment by a number of behavioral responses. The floating quiescent geckos, when resuming their active condition, responded in the same manner. The responses during flotation are similar to the behavioral reflexes triggered by a fall under normal gravity; i.e.: 1) the ventral extension of the limbs, 2) a skydiving posture, and 3) postural righting reflexes. Ventral extension of limbs was described for the first time in weightlessness. Individual variability in the frequency of flotations was found for both active and quiescent geckos during the flight. The findings show that the ability to attach to surfaces is an important factor in the geckos' adaptation to weightlessness. The behavioral responses that originated during freefall in conditions on Earth (one-G) appear as adaptations to weightlessness and remain partially effective.

A microRNA signature and TGF-β1 response were identified as the key master regulators for spaceflight response

Translating fundamental biological discoveries from NASA Space Biology program into health risk from space flights has been an ongoing challenge. We propose to use NASA GeneLab database to gain new knowledge on potential systemic responses to space. Unbiased systems biology analysis of transcriptomic data from seven different rodent datasets reveals for the first time the existence of potential “master regulators” coordinating a systemic response to microgravity and/or space radiation with TGF-β1 being the most common regulator. We hypothesized the space environment leads to the release of biomolecules circulating inside the blood stream. Through datamining we identified 13 candidate microRNAs (miRNA) which are common in all studies and directly interact with TGF-β1 that can be potential circulating factors impacting space biology. This study exemplifies the utility of the GeneLab data repository to aid in the process of performing novel hypothesis–based research.

Eight Days of Earth Reambulation Worsen Bone Loss Induced by 1-Month Spaceflight in the Major Weight-Bearing Ankle Bones of Mature Mice

Spaceflight induces bone alterations with site-specific rates of bone loss according to the weight-bearing function of the bone. For the first time, this study aimed to characterize bone microarchitecture and density alterations of three ankle bones (calcaneus, navicular, and talus) of mice after spaceflight and to evaluate the impact of 8 days of Earth reambulation. Ten C57BL/6N male 4-month-old mice flew on the Bion-M1 biosatellite for 1 month; half were euthanized within 24-h of return and half after 8-days recovery on Earth. Bone microarchitecture and quality was assessed by microtomography (μCT). Whole calcaneus bone volume fraction decreased in Flight group (-6.4%, p < 0.05), and worsened in the Recovery group (-11.08%, p < 0.01), when compared to Control group. Navicular and talus trabecular bone volume fraction showed trends toward decrease in Flight and differences reached statistical significance in Recovery group (-8.16%; -8.87%, respectively; p < 0.05) when compared to Control group. At calcaneus, cortical thickness decreased in Recovery vs. Control groups (-11.69%; p < 0.01). Bone surface area, reflecting periosteal bone erosion, significantly increased in all bone sites analyzed. Qualitative analyses of 3-D bone reconstruction revealed local sites of cortical thinning and bone erosion, predominantly at articulations, muscle insertions, and ground contact bone sites. Overall, spaceflight-induced bone loss in ankle bones was site and compartment specific whilst the tissue mineral density of the remaining bone was preserved. Eight days after landing, bone status worsened as compared to immediate return.

Development of a step-down method for altering male C57BL/6 mouse housing density and hierarchical structure: Preparations for spaceflight studies

This study was initiated as a component of a larger undertaking designed to study bone healing in microgravity aboard the International Space Station (ISS). Spaceflight experimentation introduces multiple challenges not seen in ground studies, especially with regard to physical space, limited resources, and inability to easily reproduce results. Together, these can lead to diminished statistical power and increased risk of failure. It is because of the limited space, and need for improved statistical power by increasing sample size over historical numbers, NASA studies involving mice require housing mice at densities higher than recommended in the Guide for the Care and Use of Laboratory Animals (National Research Council, 2011). All previous NASA missions in which mice were co-housed, involved female mice; however, in our spaceflight studies examining bone healing, male mice are required for optimal experimentation. Additionally, the logistics associated with spaceflight hardware and our study design necessitated variation of density and cohort make up during the experiment. This required the development of a new method to successfully co-house male mice while varying mouse density and hierarchical structure. For this experiment, male mice in an experimental housing schematic of variable density (Spaceflight Correlate) analogous to previously established NASA spaceflight studies was compared to a standard ground based housing schematic (Normal Density Controls) throughout the experimental timeline. We hypothesized that mice in the Spaceflight Correlate group would show no significant difference in activity, aggression, or stress when compared to Normal Density Controls. Activity and aggression were assessed using a novel activity scoring system (based on prior literature, validated in-house) and stress was assessed via body weights, organ weights, and veterinary assessment. No significant differences were detected between the Spaceflight Correlate group and the Normal Density Controls in activity, aggression, body weight, or organ weight, which was confirmed by veterinary assessments. Completion of this study allowed for clearance by NASA of our bone healing experiments aboard the ISS, and our experiment was successfully launched February 19, 2017 on SpaceX CRS-10.

Cohousing Male Mice with and without Segmental Bone Defects

Spaceflight results in bone loss like that associated with osteoporosis or decreased weight-bearing (for example, high-energy trauma such as explosive injuries and automobile accidents). Thus, the unique spaceflight laboratory on the International Space Station presents the opportunity to test bone healing agents during weightlessness. We are collaborating with NASA and the US Army to study bone healing in spaceflight. Given the unique constraints of spaceflight, study design optimization was required. Male mice were selected primarily because their femur is larger than females', allowing for more reproducible surgical outcomes. However, concern was raised regarding male mouse aggression. In addition, the original spaceflight study design included cohousing nonoperated control mice with mice that had undergone surgery to create a segmental bone defect. This strategy prompted the concern that nonoperated mice would exhibit aggressive behavior toward vulnerable operated mice. We hypothesized that operated and nonoperated male mice could be cohoused successfully when they were cagemates since birth and underwent identical anesthetic, analgesic, preoperative, and postoperative conditions. Using quantitative behavioral scoring, body weight, and organ weight analyses (Student t test and ANOVA), we found that nonoperated and operated C57BL/6 male mice could successfully be housed together. The male mice did not exhibit aggressive behavior toward cagemates, whether operated or nonoperated, and the mice did not show evidence of stress, as indicated by veterinary assessment, or change in body or proportional organ weights. These findings allowed our mission to proceed (launched February 2017) and may inform future surgical study designs, potentially increasing housing flexibility.

Global transcriptomic analysis suggests carbon dioxide as an environmental stressor in spaceflight: A systems biology GeneLab case study

Spaceflight introduces a combination of environmental stressors, including microgravity, ionizing radiation, changes in diet and altered atmospheric gas composition. In order to understand the impact of each environmental component on astronauts it is important to investigate potential influences in isolation. Rodent spaceflight experiments involve both standard vivarium cages and animal enclosure modules (AEMs), which are cages used to house rodents in spaceflight. Ground control AEMs are engineered to match the spaceflight environment. There are limited studies examining the biological response invariably due to the configuration of AEM and vivarium housing. To investigate the innate global transcriptomic patterns of rodents housed in spaceflight-matched AEM compared to standard vivarium cages we utilized publicly available data from the NASA GeneLab repository. Using a systems biology approach, we observed that AEM housing was associated with significant transcriptomic differences, including reduced metabolism, altered immune responses, and activation of possible tumorigenic pathways. Although we did not perform any functional studies, our findings revealed a mild hypoxic phenotype in AEM, possibly due to atmospheric carbon dioxide that was increased to match conditions in spaceflight. Our investigation illustrates the process of generating new hypotheses and informing future experimental research by repurposing multiple space-flown datasets.